Some empirical data for air slide chute conveying system design.

The air slide chute conveying system is an extreme form of airtight pneumatic conveying method, which uses low-pressure air to pass through the air slide fabrics to achieve the purpose of powder/particle conveying.
The compressed air disperses after passing through the air slide fabric and enters around the particles, which overcomes the resistance of the particles and air slide fabrics, so that the particles become to fluidization conditions like liquid, then flows by gravity in the tank.
Compared with some mechanical conveying systems, the air slide chute system with the properties of no rotating parts, no noise, convenient operation and management, light equipment weight, low energy consumption, simple structure, large conveying capacity, and easy to change the conveying direction. Very economical equipment for conveying powdery materials and granular bulk solids.

1. Construction and design
1.1, construction
The air slide chute is generally slightly inclined to the horizontal plane, and the section is usually designed with a square.
The air slide chute combined with an upper chute and lower chute, the air slide fabrics installed in the middle to make the air slide chute with two chambers, the powder material flowing in the upper chamber which is called the material chamber, and the compressed air in the lower chamber which called the air chamber.
The compressed air will be filtered and decompressed to a certain pressure as requested, then enter into the air chamber through the air pipe, and then enter into the material chamber through the air slide fabrics.
The airflow passes through the air slide fabrics and suspends the powder material to be a fluidized state, changing the friction angle of the powder material and even making the material not in contact with the air slide fabrics. However, the flow speed of the material is fast, but the frictional resistance with the air slide fabrics is very small.
Finally, the compressed air blended with the powder material will be discharged into the atmosphere through the filter, and the powder material will flow out through the discharge port of the air slide chute.
The structural materials of the air slide chute for choice can be carbon steel, aluminum alloy, stainless steel, or non-metallic materials.
Air slide fabrics can be made of different materials, such as cotton, polyester, aramid, even fiber glass, basalt, and so on. Sometimes also can be designed with microplates, such as porous ceramic plates, sintered porous plastic plates, and so on.

1.2, design and calculation.
The key contents of the design and calculation of the air slide chute conveying system include the cross-sectional size of the chute, the conveying distance, the inclination angle, the air pressure, the air consumption, and the conveying capacity.
To make the material convey normally and stably in the air slide chute, the necessary condition is that the air needs to be with a certain pressure and sufficient flow rate
1.2.1, air pressure design
The air pressure is subject to the resistance of the air slide fabrics and the height of the material being conveyed in the powder material chamber.
The air slide fabrics need to be with sufficient resistance to ensure the air distribution in the material chamber equally.
The air pressure can be determined by the following formula:
P=P1+P2+P3

P1 is the resistance of the air slide fabrics, unit is KPa;
P2 is powder material resistance, unit is KPa;
P3 is the resistance of the pipelines.
According to the experiences, the air press P always chooses between 3.5~6.0KPa, when designed, mostly according to 5.0KPa.

The air slide fabric is an important part of the air slide chute conveying system/pneumatic conveying chute, the suitable option of the air slide fabric is the precondition of the perfect performance of the air slide chute conveying system.
The air slide fabrics have to be with a pore size, uniform distribution of the weaving pattern, and good air permeability, and the pore size has to be smaller than the particles’ diameter of the powder material being conveyed to prevent the air slide fabrics be blocked.
Under stable conveying conditions, the air resistance/pressure drop across the air slide fabrics should be greater than the air resistance/pressure drop across the powder material being conveyed, and the pressure drop across the air slide fabrics have to be uniform, or the air slide chute convey system may easy to be blocked due to the problem of the air slide fabrics, so the change frequency will be much higher.

Air slide fabrics from Zonel Filtech, guarantee good performance in 12month after installation or 18 months after delivery, but when exactly operating, if the working condition is good, the good performance of the air slide fabrics from Zonel Filtech even can stand more than 4 years, which can save much maintenance cost and time for our clients.

1.2.2, compressed air consumption volume.
The compressed air consumption volume for the air slide chute conveying system is related to the following factors:
The physical properties of the material, the cross-sectional size and length of the launder, the height of the powder material layer, the inclination of the launder, etc.
To avoid the air slide fabrics being blocked, the supplied air must be de-watered and de-oiled.
The air consumption of the air slide conveying system/pneumatic conveying chute can be calculated by the following formula:
Q=qWL

“q” is the air permeability of the air slide fabric, the unit is m3/m2.h, as usual, “q” we choose 100~200;
W is the width of the powder material flow chute;
L is the length of the powder material flow chute.

1.2.3, the capacity of the air slide chute conveying system
The capacity of the air slide chute conveying system was affected by many factors, the formula can be as follows:
G=3600 X S.ρ.V = 3600 X W.h.ρ.V

S is the section area of the powder material in the air slide chute, unite is m2;
P is the air density of the fluidized material, unit is kg/m3;
V is the powder material flowing speed, unit is m/s;
W is the inner width of the air slide chute;
H is the inner height of the air slide chute.

According to the principle of fluid mechanics, the flow of powder materials in the air slide chute is very similar to the calm flow of liquid in the open channel, so the flow velocity of the powder material is related to the inclination of the air slide chute as well as the width of the air slide chute and the power material height in the air slide chute, so:
V=C√(Ri)

C is Chezy coefficient, C=√(8g/λ)
R is hydraulic radius, unit m;
“i” is the inclination of the air slide chute;
“λ” is the friction coefficient.

The inclination of the air slide chute as usual choose between 10%~20%, i.e. 6~11 degrees according to the requirements;
If the powder material chute height is H, as usual, the air slide chute width is W=1.5H, and the powder section height h is 0.4H.

2. Conclusion.
The air slide chute conveying system / pneumatic conveying chute uses low-pressure air to fluidize the material and uses the inclined component force to move the material forward. It can be widely used in the transportation of various types of air-permeable, dry powdery, or granular materials with a particle size below 3~6mm.
It has the advantages of large conveying capacity, especially low power consumption, and its application range is gradually expanding.
However due to the air slide chute being installed obliquely, the conveying distance is limited by the drop, also it is not suitable for upward conveying, so the application of the air slide chute conveying system/pneumatic conveying chute has its limitations.

Edited by ZONEL FILTECH